Search from a wide range of airlines & agents with your destination and departure city information, then tell you
airfare range for upcoming flights. The prices provided are only for your general reference and are not presented based on specific days of travel.

U.S. version. Find out when the lowest roundtrip fares published by the airlines are available.
Canada version:
Allows to specify a particular airline.
German version:
Allows to specify a particular airline and search by month.

Update:Expedia best fare tool US version and Canada version are not available any more.
Only German version is still available.